This invention relates in general to load or weighing scales used to measure the weight of a wheeled vehicle or trailer, and more particularly to load scales which are self-contained and portable as opposed to being installed in a fixed, in-ground installation. Even more particularly, the invention relates to such scales which comprise a drive-on base platform suitable for use on relatively rugged and uneven terrain without underlying concrete slabs, poured floors or road surfaces.
Scales for determining the total weight of a loaded truck or trailer where the vehicle or trailer is driven onto the load scale such that the wheels of the vehicle or trailer are positioned on the scale are well known. Some such scales are permanently installed in a roadbed, such as the weigh stations found along interstates. There are many other circumstances in which vehicle or trailer load weights need to be determined where a permanent installation is not warranted or possible, and for this purpose portable or stand-alone load scale platforms have been developed. These portable scales typically comprise a base or foundation platform with ramps on two opposing sides and a "floating" support deck or weight platform mounted a short distance above the base platform on a plural number of compressible scale devices known as load cells. When a wheeled vehicle is driven up the ramp and the wheels positioned on the support deck, the support deck and load cells are compressed relative to the base platform and provide an indication of the weight of the load through electronic metering and indicator means. Usually four load cells are symmetrically positioned beneath the support deck.
Examples of such load scales can be seen in U.S. Pat. No. 3,933,212 to Bradley et al., U.S. Pat. No. 4,203,497 to Harris et al., U.S. Pat. No. 4,453,606 to Mokhbery et al., and U.S. Pat. No. 4,979,581 to Kroll. The constructions of these load scales presuppose that the scales will be used on a flat and level concrete slab or other suitable floor-like surface, and as such little consideration has been given to outdoor or off-surface applications. Use of a load scale placed directly on uneven ground without an underlying support slab requires a construction which is not much addressed in the known devices, as most previous devices are not sufficiently strong to stand alone without underlying support. In addition, some of the known devices have solid, co-extensive foundation or base plates which require a flat surface in order for the device to properly function, meaning that the ground must be prepared prior to use and the devices cannot be employed where roots or rocks are present. Any uneven in the ground underneath the load scale causes the scale to flex and torque, resulting in inaccurate weight readings, sometimes to such an extent that the readings are useless. There is a great need for easily portable load scales suitable for use on rugged terrain at varying locations. For example, log trailers loaded in the field are not allowed to carry more than a predetermined maximum load and overloading can result in the assessment of fines. Without a scale at the loading site, the loader operators must make estimates as to the total weight, and typically under-load the trailer by a substantial amount to provide for a margin of error. This results in lost profits as each trailer load is not maximized.
Some prior art addresses the problems associated with placement of a portable load scale onto uneven terrain or the problems of asymmetrical loading by presenting somewhat complicated mounting systems. Examples of these devices are shown in U.S. Pat. No. 5,600,104 to McCauley et al., U.S. Pat. No. 4,828,055 to Hamilton et al., U.S. Pat. No. 4,134,467 to Czyryk, U.S. Pat. No. 4,545,622 to Leiman, U.S. Pat. No. 4,554,987 to Dillon, U.S. Pat. No. 4,281,728 to Dickason et al., and U.S. Pat. No. 4,148,371 to Nelson. McCauley et al. utilizes a spherical ball bearing support with loosely mounted vertical bolts which allow for relative angular movement. Hamilton et al. uses pins, rollers and slots. Czyryk uses a ball and socket arrangement. Leiman uses pivoting chairs and roller supports. Dillon uses rocking posts with curved bottoms and tops. Dickason et al. uses pivot pins. Nelson uses levers mounted on pivot pins.
It is an object of this invention to provide a portable load scale which can be used without an underlying slab or support structure, such that the load scale can be placed directly onto the ground and will perform on relatively rugged and uneven terrain. It is a further object to provide such a load scale where the weigh platform is mounted onto the base platform such that the load cells are attached directly to the weigh platform, with the cells attached to a rocker member containing a ball bushing to reduce friction and allow relative motion in three dimensions, with the rocker assembly retained in a bracket chair attached to the base platform by a pin inserted through the bushing. It is a further object to provide such a load scale where the base platform is constructed to provide high structural rigidity when a wheeled vehicle or trailer is driven onto the scale, where opposing ramps are connected by a pair of runner assemblies aligned so as to be directly under the vehicle wheels as the wheels pass on, across and off the scale. It is a further object to provide such a scale where the floating support deck is extremely rigid and where the bottom of the support deck is maintained a sufficient distance above the ground and the base plates of the runner assemblies such that any debris which falls between the support deck and ground or base plate will not impair the vertical movement of the scale. It is a still further object to provide such a load scale where the load information ascertained by the load cells may be transmitted by radio frequency to a visible read-out device or by direct wire connection, such that the read-out device can be located in the most desirable location, such as in the cab of a loader separate from the truck or trailer, and can be easily relocated in different loaders if needed.